Nuclear reactors can be used to power electricity generating plant machinery, usually in the form of the generation of steam to power steam turbines. The steam turbines can then be used to drive turbo-alternators for electricity generation.
In such arrangements there is a need to control the dissipation of excess or waste heat produced by the nuclear reactor. This is usually achieved by the circulation of cooling water feeds through the reactor assembly.
While effective at the dissipation of heat, such cooling water systems must be resistant to leaks and power outages. Pumps are typically used to inject water into the coolant circuit to compensate for losses and leakage. These pumps are required to be capable of operating in the absence of external power, such as during electricity supply outages.
It is known to use electrically powered coolant circulation and make-up pumps. In such instances, the electrical power supplies need to be of high integrity. This in turn requires the presence of a high integrity back-up electrical supply, typically in the form of a diesel engine powered electricity generating unit.
Such generating units have many potential causes of failure including inter alia loss of engine lubricant or coolant, fuel supply exhaustion, fuel contamination, filter blockages, ignition failure, enclosure ventilation failure and control system failures.
As a result, diesel engine powered generating sets require testing at regular intervals, often as part of a routine maintenance plan. The requirement for regular maintenance and testing can result in problems caused by human error.
Typically diesel engine powered generating sets are configured to generate electricity which is used to energise bus bars and then operate electrically powered pumps. These electrical systems may also be a further source of unreliability.
An alternative approach is to use a diesel engine powered back-up coolant circulation pump. However, such arrangements have similar drawbacks to those outlined above for diesel engine powered generating sets.